How does S Pen (Samsung) show cursor on screen?

Break it down-How does the S pen work? offers a nice explanation along with a link to video too

• S pen pulls power from the device wirelessly



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  Electromagnetic field that provides power to the pen can also be used to calculate its position relative to the screen. This, along with information from the S Pen button and the nib on the end are what is used to determine what the user it doing with the S Pen.

  
  



• Pressure sensitivity is built in the stylus


• To summarize
  
  

  
  

  An electromagnetic field is generated from a circuit behind the screen. The S Pen picks this up and uses it to power itself and figure out its position relative to the screen. It sends this, along with information from the S Pen button and the nib at the end, back to the Note.

  
  

Edit: Video in linked post makes it clear ascend easy to understand